The present invention generally relates to a circuit for reading signal from a digital rotary switch, and in particular to a circuit for reading signal from a rotary switch type volume knob mounted on a multi-medium keyboard of a computer.
A keyboard is a commonly used input device for computers or other processor-based electronic devices. There are a variety of keyboards available in the market suitable for different needs and requirements. A multi-medium keyboard is particularly for use with a multi-medium computer and the associated software. Besides regular keys, the multi-medium keyboard further comprises control means for controlling audio and video output of the computer. For example, the multi-medium keyboard may comprise a volume control knob to be manually turned for controlling the audio output of the computer.
The volume control knob is usually comprised of a digital rotary switch mounted on the keyboard. When rotated, the rotary switch generates two or more pulses at terminals thereof which are applied to a microprocessor-based signal processing circuit of the keyboard. The signal processing circuit calculates a phase difference between the pulse signals for establishing a corresponding volume control signal to be transmitted to a computer.
To read the pulse signals, two pins of the microprocessor have to be exclusively used to receive the pulses. This imposes constraints in designing the circuit of the keyboard. Furthermore, it also hinders reduction of cost of the keyboard circuit.
Thus, it is desired to have a rotary switch signal reading circuit having a simplified circuit configuration for addressing the above problems.
Accordingly, an object of the present invention is to provide a rotary switch signal reading circuit which are coupled to a key signal reading array of a microprocessor of a keyboard without additional use of pins of the microprocessor thereby simplifying circuit layout and reducing costs thereof.
To achieve the above object, in accordance with the present invention, there is provided a digital rotary switch signal reading circuit adapted to read volume control signal from a volume control knob mounted on a multi-medium keyboard. The rotary switch has two signal terminals and one common terminal. The signal terminals are connected to two of input pins of a microprocessor of the keyboard and the common terminal is connected to one of the output pins of the microprocessor, the input pins and the output pins being interconnected with each other to form a key array. Thus, the signal from the rotary switch may be read by the computer in the same way as key actuation signal from the key array.